1. The Field of the Invention
The invention relates to a method and a corresponding communication system for discovering and synchronizing service capabilities, in particular a method for discovering and synchronizing service capabilities between user equipment and a cellular telecommunications network, particularly an LTE network.
2. The Relevant Technology
Mobile telecommunication systems have evolved from circuit-switched techniques to packet-switched information exchange. In 3rd generation mobile cellular systems like UMTS, i.e. in the Universal Mobile Telecommunications system, voice connections as well as non-voice connections are implemented as packet-switched services. A plurality of services have been implemented, wherein many of these are designed for providing so-called multimedia services. The so-called IP multimedia subsystem (IMS) has been designed to enable connections between conventional cellular communication systems like UMTS or even GSM with IP-based networks, i.e. networks implementing the packet-oriented IP standard. Basically the IMS uses the so-called Session Initiation Protocol (SIP) for establishing and controlling communication sessions between multimedia devices.
Voice over LTE (VoLTE) is a service that provides voice and video services over an LTE system using the IP multimedia subsystem (IMS). The VoLTE system is based on the MMTel, i.e. the MultiMedia Telephony service, which provides fixed and mobile real-time multimedia communication. In contrast to legacy circuit switched telephony services MMTel uses an IP-based transport over the mobile access.
To make full use of the capabilities provided by a radio terminal and a communications network, the capabilities have to be synchronized between the entities. In other words, the use of a particular service of a telecommunications system requires compatibility of all entities implementing that service. Since radio terminals and telecommunication networks may differ in properties and capabilities, the radio terminal and the telecommunications network have to ensure that the desired service is supported by the entities, i.e. the radio terminal and the telecommunications network have to explore and synchronize each other's capabilities.
In one embodiment the Communication Waiting (CW) service is of interest. The 3GPP specifications have specified two mutually exclusive technical options to implement the Communication Waiting (CW) supplementary service with the technical specification TS 24.615, i.e. namely a ‘terminal based’ method and a ‘network based’ method. In a terminal
However, the GSMA PRD IR.92 specification is the industry standard for terminal, network and network service vendors that mandates which aspects of the 3GPP/IETF standards shall be used to deploy voice, video and SMS services over VoLTE. The implementation of the Communication Waiting service method mandated/required by the IR.92 is the ‘terminal based’ method, which only now has identified limitations to using this ‘terminal based’ approach, e.g. multi-SIM services, SIM swap scenarios and multi device scenarios.
For example, when terminal based communication waiting is used in a multi device scenario, a plurality of at least two devices, e.g. IR.92 compliant radio terminals, share a single, common set of network services, where each of the devices may respond to an incoming call. When one of the devices is busy, i.e. a voice call is already established to one of the devices, another incoming call will be signaled to both devices, i.e. the network will signal the incoming call to both devices. The user may then either accept or decline the call. The user may also configure the settings of the device or devices to allow a call-waiting tone to be signaled in this “communication waiting” case. The network only conveys messages between the caller radio terminal and the called radio terminal but does not need to have any knowledge about the status of the called radio terminal, i.e. the network does not need to know if the called radio terminal is in a busy state. So in the ‘terminal based’ scenario each of the devices operates as a separate entity, i.e. the communication waiting service is configured locally to the device, and must be configured separately for each service, i.e. the entire management of the “communication waiting” service is performed by the devices. Accordingly, when using the ‘terminal based’ approach, there is no mandate for information to be available in the network that allows to manage such services for all devices assigned to one MSISDN/user.
Problems of this kind, e.g. the management of user settings for the Communication Waiting service or similar services, can be solved by using the ‘network based’ approach to implement the Communication Waiting service.
However, current VoLTE deployments of devices and networks are too advanced to change network and device support for implementing the Communication Waiting or a similar service. Also, a simple change to the standards is not enough to solve above identified problems, because a design should provide backwards compatibility between devices and/or networks which only support the ‘terminal based’ CW, whilst providing the preferred solution for those devices and networks which both support the ‘network based’ approach. As a consequence a common solution is required within the industry.
Both networks and devices need to behave differently depending on whether the ‘network based’ or the ‘terminal based’ approach of a service, e.g. the “Communication Waiting” service, is utilized. Today, devices and networks are mandated to deploy the “terminal based” method only. However, it is a target to have full device and network support for the “network based” method to avoid above described issues. But until then, over time there will be a mix of devices which support the terminal based method only, and ones supporting both with backwards compatibility, as well as networks that support the terminal based method only and networks that support both methods with backwards compatibility.
Hence, there is a need for a method and system whereby a device, i.e. a radio terminal, and network can mutually discover support for the network based method, in order to know how the optimal method to invoke a service, e.g. the Communication Waiting supplementary service.